Grain boundary television camera tube



United States Patent Office 3,121,186 Patented Feb. 11, 1964 Filed Jan. 6, 1961, Ser. No. 81,161 4 Claims. (Cl. 315-16) This invention relates generally to television camera tubes, and pertains more particularly to a camera tube utilizing a mosaic of grain boundary detectors.

-In order to provide a ready understanding of the benefits to be derived from a practicing of the instant invention, it will be well to refer briefly to prior art devices of the general character with which the present invention is concerned. For instance, in using conventional vidicons, the imaging screen consists of a transparent conductive coating which faces the radiation source and the layer of photoconducting material which has a suitable response characteristic. The conductive material and the opposite face of the photoconductive material form two plates of a condenser with the photocond-uctive material acting as a leaky dielectric. The amount of leakage current passing through any given region of the photocond-ucting dielectric is dependent upon the amount of radiation falling on that region. In practice, the back of the photoconductor is negatively charged by scanning with an electron beam. Further scanning then recharges those parts of the surface which have been either fully or partially discharged by incident radiation, the information as to the amount of discharge being contained in the charging current or in the reflected current which may be amplified by secondary emission multipliers. The maximum time allowed between successive scans, or to say it another way, the maximum time which the screen will retain an image is limited by the dark current of the photocond-uctor. This time is of the order of seconds in currently available models.

In contradistinction to the prior art device alluded to above, the present invention makes use of a mosaic or multiplicity of grain boundary detectors. The electron beam is deflected from one detector to another in a successive manner so as to cover the entire plurality of detectors and thereby produce an image corresponding to the image that has been impressed upon the overall mosaic of detectors. Not only does the instant invention have for an object the facile and economical production of such a detector which is capable of picking up and reproducing a faithful image, but the invention has for an additional important aim the production of such images that may be formed and retained for a period of time considerably longer than that which has been possible in the past. Also, the invention has for an object thepro-duction of at detecting device for television purposes that is exceptionally simple and of a character that will not get out of order very readily. 7

Other objects will be in part obvious, and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

In the drawing:

The single figure that has been present represents a schematic perspective view showing an imaging tube equipped with a mosaic of grain boundary detectors constructed in accordance with the teachings of the present invention.

Referring now in detail to the drawing, it will be observed that the television camera tube has been indicated in its entirety by the reference numeral 10'. As is conventional with imaging tubes of this type a glass envelope has been depicted which appears largely in a section, the reference numeral 12 identifying this envelope. Contained within the envelope at one end thereof is a conventional electron gun 14. The gun 14 includes a heating filament 16 for a cathode 18. Also included as part of the gun 14 is a control grid 29 and a plurality of accelerating anodes labelled 22. The cathode 18 is of course responsible for emitting the electron beam denoted by the reference numeral24 and the grid it} controls the beam to the extent of cutting the beam off at prescribed intervals. The accelerating anodes 22, as their name implies, cause acceleration of the electrons constituting the beam 24. The anodes receive their appropriate potentials from a potentiometer 26 which may be appropriately energized, such as by means of a battery 28. For the purpose of turning the beam 24 on and off and also for synchronizing the beam for telecasting purposes, a blanking and synchronizing timing generator 39 is employed.

The beam 24 is directed from the electron gun 14 toward the opposite end of the camera tube 1% and is caused to impinge upon a plate or sheet of semi-conductive material labelled 32. Various semi-conductive materials may be utilized in the construction of the plate 32, silicon, germanium and indium-antimonide being but several of the materials that might be employed. The heart of the invention resides in the provision of a grain boundary 34 intermediate the generally parallel faces of the plate 32. Although grain boundaries are now fairly well understood, there being considerable printed literature describing same as Well as various patents, if additional information is desired in this instance it is suggested that reference be had to Transient Response of Grain Boundaries and Its Application for a Novel Light Sensor authored by Rolf K. Mueller and which article appears on page 1004 of the July 1959 issue of The Journal of Applied Physics. In order to divide the plate 32 into a multiplicity of islands a plurality of horizontally extending grooves 36 and a plurality of vertically directed grooves 38 are formed in the face of the plate 32 nearer the viewer. These grooves may be etched or mechanically cut so as to pro-. vide the various islands or individual units which have been denoted by the reference numeral 49. It will also be observed by examining the edges of the plate 32 that the grooves extend sufficiently inwardly so as to intersect the boundary 34. Thus, what We have are intersecting grooves 36 and 38 on one face of the plate 32, these grooves extending inwardly so as to meet the grain boundary .34. Consequently, the grain boundary 34 is divided into a number of individual areas which have been referred to as the islands 40.

For the purpose of deflecting the electron beam 24 so as to cause it to impinge on the various islands 40, horizontal deflecting coils 42 are used in conjunction with vertical deflection coils 44. The means by which such a deflection is produced is old and well known, there being shown in the drawing an x scanning circuit 46 and a similar y scanning circuit 48. Through such an arrangement, the electron beam 24 can be caused to scan the grooved face of the plate 32. In the figure that has been presented in order to exemplify the invention, it will be observed that the electron beam 24- is shown in striking engagement with the upper lefthand island 4-0. The circuit back to the cathode 18 is completed through a video amplifier 5t) which is in series with the battery or source of power 23. As is conventional in the vidicon type of tube, a signal output circuit 52 is connected to the video amplifier 50. It will be appreciated, though, that a secondary emission multiplier arrangement may be used instead of the more simplified amplifying arrangement that has been pictured. Such a multiplying arrangement has been used quite extensively in conjunction with image orthicons. The direct current measurement which has been disclosed above has been more Widely employed in connection with vidicons. It might be explained that when secondary emission is utilized that the electron beam is reflected by the electric field at the surface of target plate 32. In this case, one requires a second beam for erasing the image from the target plate or screen.

Having presented the foregoing description, the operation of our camera tube should be readily understood. The incident radiation that is to form the image on the semiconductive sheet or plate 32 has been designated by the arrows 54. Whereas each cell unit comprised of an island 40, the portion of grain boundary coextensive therewith and the unit of area on the forward face receiving the radiation 54 has had its grain boundary portion precharged by the previous passage of the electron beam 24 over the various islands 49, the charge or potential barrier of any grain boundary is reduced by the hole injection provided by the incident radiation. The greater the radiation, the greater will be the decrease in charge. Thus, if the unit area of the forward face which is aligned with the upper lefthand island 41; receives a considerable number of photons, the charge on the grain boundary in that region will be decreased accordingly. Consequently, the next passage of the electron beam 24 thereover will cause a considerable number of electrons to flow and the output from the amplifier 51') will be relatively large. On the other hand, should the next unit area receive little or no light, when the electron beam 24 impinges on the island 442 just to the right of the upper lefthand island, little or no output from the amplifier 56) will result. By scanning all of the islands 44 it will be appreciated that a raster will have been produced and by reason of the changes in the beam current, the requisite image will have been produced.

One outstanding advantage of the grain boundary screen is that at liquid nitrogen temperatures and below, the semiconductive plate 32 -will integrate the incoming radiation 54 and will retain the resulting image for periods up to several days with but little deterioration. This means that the grain boundary screen could be used for either long or short persistence, depending upon the temperature to which it was subjected. Therefore, the present invention is appreciably more flexible in its application than the photoconductive screens of the prior art. It might be mentioned that the wavelengths of the incident radiation 54 to which the grain boundary detector or plate 32 will respond will be determined by the type of semiconducting material that is employed just as the type of photoconducting material determines the response of conventional screens.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed:

1. A television camera tube comprising an evacuated envelope, an electron gun for generating an electron beam Within said envelope, a plate of semiconductive material having a grain boundary located between the opposite faces thereof, said plate having a plurality of grooves separating said grain boundary into a multiplicity of discrete grain boundary regions, means for deflecting said electron beam so that it sweeps over one face of said plate, the other face of said plate being subjected to incident radiation, and means for determining the variations in electron beam intensity due to said incident radiation.

2. A television camera tube comprising an evacuated envelope, an electron gun for generating an electron beam within said envelope, a plate of semiconductive material having a grain boundary located between the opposite faces thereof, the face earer said electron gun having a plurality of intersecting grooves extending inwardly to said grain boundary to provide a multiplicity of islands, means for deflecting said electron beam so that it sweeps from island to island, means connecting the other face of said semiconductive plate in circuit with said electron gun, and means for indicating the intensity of said electron beam as influenced by the degree of charge on various portions of said grain boundary resulting from the amount of light striking said other face.

3. A television camera tube comprising an evacuated envelope, a plate of semiconductive material having a grain boundary located between the opposite faces and having a plurality of grooves separating said grain boundary into a multiplicity of discrete grain boundary regions, means mounted within said envelope for generating an electron beam to precharge said grain boundary, means for deflecting said electron beam to sweep said beam over one face of said plate While the other face of said plate is subjected to incident radiation, means for interconnecting said other face with said means for generating, and means for indicating variations in intensity of said electron beam due to variation in said incident radiation striking said other face as said beam sweeps over said one face.

4. A television camera tube having an evacuated envelope comprising a plate of semiconductive material having a grain boundary located betwen first and second faces and having a plurality of intersecting grooves in said first face separating said grain boundary into a plurality of discrete grain boundary regions, means mounted Within said envelope for generating and casting an electron beam on said first face to precharge said grain boundary, means for deflecting said electron beam to sweep said beam over said first face while incident radiation impinges on said second face, means for interconnecting said second face with said means for generating, means for indicating variations in intensity of said electron beam due to variations in said incident radiation striking said second face as said beam sweeps over said first face, and means for intermittently terminating generation of said beam.

References Cited in the file of this patent P. K. Weimer: RCA Technical Notes No. 132, Solid State Image Intensified Pickup Tubes.

R. K. Mueller: Journal Of Applied Physics, Transient Response of Grain Boundaries and Its Application for a Novel Light Sensor, p. 1004, July 1959. 

1. A TELEVISION CAMERA TUBE COMPRISING AN EVACUATED ENVELOPE, AN ELECTRON GUN FOR GENERATING AN ELECTRON BEAM WITHIN SAID ENVELOPE, A PLATE OF SEMICONDUCTIVE MATERIAL HAVING A GRAIN BOUNDARY LOCATED BETWEEN THE OPPOSITE FACES THEREOF, SAID PLATE HAVING A PLURALITY OF GROOVES SEPARATING SAID GRAIN BOUNDARY INTO A MULTIPLICITY OF DISCRETE GRAIN BOUNDARY REGIONS, MEANS FOR DEFLECTING SAID ELECTRON BEAM SO THAT IT SWEEPS OVER ONE FACE OF SAID PLATE, THE OTHER FACE OF SAID PLATE BEING SUBJECTED TO INCIDENT RADIATION, AND MEANS FOR DETERMINING THE VARIATIONS IN ELECTRON BEAM INTENSITY DUE TO SAID INCIDENT RADIATION. 